Apparatus And Method For Executing The Handoff Process In Wireless Networks

ABSTRACT

Disclosed is an apparatus and method for executing the handoff process in the wireless networks. The apparatus comprises a processor to execute an identity checking mechanism. When a wireless network station wants to move from a source AP to a destination AP, the wireless network station sends an authentication request message to the destination AP. The identity checking mechanism searches a R 0 KH table of the destination AP for the R 0 KH ID contained in the authentication request message, and determines a setting parameter for executing a handoff process. Thereby, the wireless network station may execute the handoff process. A R 0 KH table of an AP consists of all IDs of R 0 KHs that can be accessed by the AP.

FIELD OF THE INVENTION

The present invention generally relates to an apparatus and method forexecuting the handoff process in the wireless networks.

BACKGROUND OF THE INVENTION

The wireless networks are an important medium for connecting toInternet. The wireless network is more prone to tapping and theft incomparison with the wired network. Between an access point (AP) and awireless network station, the use of security key for authentication andencryption is an important issue for wireless networks. If the AP andthe wireless network station do not save the security key in advance,the key will cause the execution of a handoff process when the wirelessnetwork station connected to an AP.

Because the handoff process takes much time, the execution of thehandoff process may interrupt the real-time application, such as voiceover IP (VoIP). IEEE802.11r protocol defines three-level keyarchitecture to accelerate the execution of handoff process and generatesecurity key.

FIG. 1 shows a schematic view of an exemplary three-level keyarchitecture of IEEE802.11r protocol. Referring to FIG. 1, the firstlevel key is Pairwise Master Key R0, or PMK-R0. PMK-R0 is generated bythe first level Master Session Key (MSK) or Authentication,Authorization and Accounting (AAA)-key, and is saved at a wirelessnetwork station 101 and a R0 key holder (R0KH). MSK is generated andseparately by wireless network station 101 executing the handoff processand by AAA server 103 executing IEEE802.1X authentication. R0KH playsthe role of AAA client to receive and store the MSK from AAA server 103.

The second level key PMK-R1 is stored at wireless network station 101and a R1 key holder (R1KH). PMK-R1 is generated by PMK-R0. PMK-R1 may beused to generate the third level Pairwise Transient Key (PTK). The PTKis the key for message encryption and decryption between wirelessnetwork station 101 and the APs inside the third level.

The aforementioned IEEE802.11r three-level key architecture defines themobility domain (MD) architecture. As shown in FIG. 1, an MD includes aplurality of R0KHs at first level 131. Each R0KH has connections to aplurality of R0KHs, for R1 from all the R0KHs in the MD, for example,R1KH₁ and R1KH₂ may obtain PMK-R1 directly from R0KH₁, or indirectlyfrom R0KH₂. Second level 132 is all the R1KHs. Third level 133 is allthe APs of an MD in the following description.

Based on the MD architecture defined in IEEE802.11r protocolspecifications, the movement of the wireless network station may bedivided into intra-MD movement and Inter-MD movement. The intra-MDmovement may be further divided into intra-R1KH movement and inter-R1KHmovement. For example, wireless network station 101 switching from AP₀to AP₁ is an intra-R1KH movement, and switching from AP₁ to AP₂ or AP₃is an inter-R1KH movement. These two examples are both intra-MDmovements within domain 110. On the other hand, a switching from AP₃ inMD 110 to AP₄ in MD 120 is an inter-MD movement.

When moving in MD, a wireless network station needs to execute a fastbasic service set (Fast BSS) handoff process. For inter-MD movement, thewireless network station needs to execute initial MD association handoffprocess. Through the MD Identity (MDID) embedded in the periodicalbroadcast of probe and beacon messages by the AP, it is possible todistinguish the inter-MD movement from intra-MD movement.

The current MDID can be assigned by each vendor; however, there is noguarantee that the MDID assigned by different vendors will be unique.Therefore, when a wireless network station executes inter-MD movement,the inter-MD movement may be mistakenly identified as an intra-MDmovement because of the same MDID, and then the Fast BSS handoff processis executed. In this scenario, during the execution of Fast BSS handoffprocess, the AP cannot generate PTK because the R1KH cannot obtainPMK-R1 from R0KH used by the wireless network station. Therefore, the APwill notify the wireless network station to terminate the Fast BSShandoff process, and to execute the initial MD association handoffprocess.

FIG. 2 and FIG. 3 show the exemplary flowcharts of initial MDassociation handoff process and the Fast BSS handoff process,respectively.

In FIG. 1, when wireless network station 101 turns on the wirelessnetwork function, wireless network station 101 can connect to thewireless network through AP₁ of MD 110, or move from MD 120 to thecoverage range of AP₁, which can be known from the probe and beaconmessages broadcast by AP₁ to be an inter-MD movement. Wireless networkstation 101 executes the initial MD association handoff process in FIG.2.

In step 201A and step 201B, wireless network station 101 and AP₁ executethe open system authentication process. In step 201A, wireless networkstation 101 transmits authentication request to AP₁. In step 201B, AP₁replies the authentication response to wireless network station 101.After the open system authentication process finishes, AP₁ allowswireless network station 101 to transmit IEEE802.11r communicationprotocol messages to AAA server.

Steps 202A & 202B are association request and association response,respectively. In step 202A, wireless network station 101 transmitsassociation request to AP₁, where the field of the mobility domaininformation element (MDIE) of the association request message is set as“0” to indicate that wireless network station 101 supports Fast BSShandoff process. In step 202B, AP₁ uses association response message tostore the R0KH₁, R1KH₁ and MDID in the MDIE field, and transmits theassociation response message to wireless network station 101.

In step 203, wireless network station 101 executes the IEEE803.1Xauthentication to AAA server 103 through AP₁. After the authenticationstep is successful, wireless network station 101 and AAA server 103generate the MSK respectively, and AAA server 103 will transmit the MSKto R0KH₁.

Steps 204A & 204B are to generate PMK-R0 and PMK-R1, respectively. Instep 204A, wireless network station 101 and R0KH₁ execute the keyderivation function (KDF) algorithm, respectively, to use R0KH₁ withMSK, and the MAC address of wireless network station 101 to generatePMK-R0. In step 204B, PMK-R1 may be generated by using PMK-R0, MACaddress of wireless network station 101, and ID of R1KH₁.

In step 205, wireless network station 101 and AP₁ execute the 4-wayhandshake of IEEE802.11i to generate PTK. In this step, wireless networkstation 101 and AP₁ generate a random number “SNonce” and a randomnumber “ANonce”, respectively, and exchange. AP₁ transmit the two randomnumbers “SNonce” and “ANonce”, ID of R0KH₁, MAC address of wirelessnetwork station 101 and MAC address of AP₁ to R1KH₁. Then, wirelessnetwork station 101 and R1KH₁ execute KDF algorithm, respectively, anduse the above parameters, ID of R1KH₁ and PMK-R1 to generate PTK. Aftergenerating PTK, R1KH₁ transmits the PTK to AP₁.

After executing the above initial MD association handoff process,wireless network station 101 is successfully connected to AP₁, and R0KH₁and R1KH₁ will store PMK-R0 and PMK-R1, respectively. PMK-R0 and PMK-R1may be used to generate a new PTK. Therefore, the time-consumingIEEE802.1X authentication process may be saved to reduce the handoffprocess time.

When the wireless network station moves within MD₁, for example, fromAP₁ to AP₃, the wireless network station may execute the Fast BSShandoff process of FIG. 3.

Because AP₁ and AP₃ are both in MD₁, in step 301A, wireless networkstation 101 notifies AP₃ through the fast transition (FT) authenticationrequest message to execute FT authentication. The authentication requestmessage includes a random number SNonce for generating PTK, and an MDIEfield. The MDIE field includes the IDs of R0KH₁, R1KH₁, and MDID of MD₁.

AP₃ knows of the occurrence of the inter-R1KH switch from theauthentication request message, and replies an authentication responsemessage to wireless network station 101, as shown in step 301B. Theauthentication response message includes a random number ANonce forgenerating PTK, and an MDIE field. The MDIE field at least includes theIDs of R0KH₂, R1KH₃, and MDID of MD 110.

After receiving the FT authentication response message from AP₃,wireless network station 101 uses random number ANonce and MDIE, andwith ID of R1KH₃, MAC address of wireless network station 101 and PMK-R0to generate PMK-R1. The PMK-R1 will be stored in wireless networkstation 101 and R1KH₃. Then, step 302 is to generate PTK according toMAC address of wireless network station 101, MAC address of AP₃, SNonce,ANonce, and IDs of R0KH₁ and R1KH₃. If wireless network station 101moves from AP₁ to AP₀, the old PMK-R1 may be used directly to generatePTK because AP₁ and AP₀ are connected to the same R1KH.

As shown in step 303, AP₃ transmits MAC address of wireless networkstation 101, MAC address of AP, SNonce, ANonce, ID of R0KH₁ to R1KH₃ forgenerating new PTK.

In step 304, according to the ID of R0KH₁, R1KH₃ requests PMK-R1 fromR0KH₁. However, if wireless network station 101 moves from AP₁ to AP₀,this step may be omitted.

After obtaining new PMK-R1, R1KH₃ executes KDF algorithm to generatenetwork station 101 and AP₃ both have the same PTK.

Wireless network station 101 and AP₃ then execute step 306 for resourcefrom AP₁ to AP₃. In this manner, wireless network station 101 may startto use AP₃ service.

In the Fast BSS handoff process, the PMK-R0 is re-used to generate newPTK to accelerate the handoff process. Because the AP will broadcast theprobe and beacon response frame with the IDs of R0KH and R1KH used bythe AP and the ID of MD embedded in the frame, the appropriate handoffprocess may be selected after the wireless network station selects theAP, and whether the movement is an Inter-MD movement or an intra-MDmovement is determined. Especially, the MAC address may be used toidentify R0KH and R1KH, and MDID is managed by the vendors.

SUMMARY OF THE INVENTION

In accordance with the exemplary embodiments of the present invention,the disclosed is directed to an apparatus and method for executing thehandoff process in wireless networks. Without MDID for executing handoffprocess, the uncertainty of MDID may be ruled out. In the presentdisclosure, each AP stores a R0KH table, and the R0KH table records theIDs of all the R0KHs at the AP.

In an exemplary embodiment of the present invention, the disclosed isdirected to an apparatus for executing handoff process in wirelessnetwork. The apparatus comprises a processor to execute an identitychecking mechanism. The R0KH table of a destination AP consists of theIDs of all the R0KHs accessible within the coverage of the destinationAP. When a wireless network station wants to move from a source AP to adestination AP, the wireless network station sends an authenticationrequest message to the destination AP. The identity checking mechanismsearches the R0KH table of the destination AP for the R0KH ID containedin the authentication request message, and determines a settingparameter for executing a handoff process. Thereby, the wireless networkstation may execute the handoff process.

In another exemplary embodiment of the present invention, the disclosedis directed to a method for executing handoff process in wirelessnetworks, applicable to the movement of a wireless network station. Whena wireless network station wants to move from a source AP to adestination AP, the method comprises: a wireless network stationtransmitting an authentication request message to the destination AP,the authentication request message including an R0KH ID; using the R0KHID to search the R0KH table of the destination AP for selecting atransition process, the R0KH table of destination AP including the IDsof all the R0KHs accessible to the destination AP; when the R0KH ID notin the R0KH table, executing an initial MD association handoff process;and when the R0KH ID in the R0KH table, executing a Fast BSS handoffprocess.

The foregoing and other features, aspects and advantages of the presentinvention will become better understood from a careful reading of adetailed description provided herein below with appropriate reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of an exemplary 3-level key architectureof IEEE802.11r communication protocol.

FIG. 2 shows a schematic view of an exemplary flowchart of a wirelessnetwork station executing initial MD association handoff protocol.

FIG. 3 shows a schematic view of an exemplary flowchart of a wirelessnetwork station executing Fast BSS handoff protocol.

FIG. 4 shows a schematic view of an exemplary R0KH table, consistentwith certain disclosed embodiments of the present invention.

FIG. 5 shows a schematic view of an exemplary apparatus for executinghandoff process in a wireless network, consistent with certain disclosedembodiments of the present invention.

FIG. 6 shows an exemplary schematic view of the R0KH tables stored atsource AP and destination AP for a wireless network station to executean inter-MD or an Intra-MD movement, consistent with certain disclosedembodiments of the present invention.

FIG. 7 shows a schematic view of an exemplary flowchart of the methodfor executing handoff process in wireless networks, consistent withcertain disclosed embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosed embodiments in accordance with f the present invention mayprovide an apparatus and a method for the AP to select the suitablehandoff process for the wireless network station without using the MDIDto avoid the MDID collision. In the disclosed embodiments, each APstores a R0KH table with all the R0KH IDs. When the wireless networkstation moves from an AP to another AP, the present invention may helpthe wireless network station to select a suitable handoff process bysearching the R0KH table. The movement of the wireless network stationmay be either inter-MD movement or intra-MD movement.

Take the 3-level key architecture of IEEE802.11r communication protocolin FIG. 1 as an example. The R0KH table of the present invention may bedescribed as in FIG. 4. Because in the architecture of FIG. 1, the R0KHID holders of MD 110 are R0KH₁ and R0KH₂ of first level 131, therefore,each AP of MD 410 of FIG. 4, i.e., AP₀, AP₁, AP₂, AP₃, stores a R0KHtable 415 consisting of R0KH₁ ID and R0KH₂ ID. Similarly, in thearchitecture of FIG. 1, the R0KH ID holder of MD 120 is R0KH₃,therefore, each AP of MD 420 of FIG. 4, i.e., AP₄, AP₅, stores a R0KHtable 425 consisting of R0KH₃ ID.

With the R0KH table, each AP may select the suitable handoff process forthe wireless network station without MDID. FIG. 5 shows a schematic viewof an exemplary apparatus for executing handoff process in a wirelessnetwork, consistent with certain disclosed embodiments of the presentinvention.

Referring to FIG. 5, an apparatus 500 comprises a processor (not shown)for executing an identity checking mechanism 525. When a wirelessnetwork station 501 wants to move from a source AP 561 to a destinationAP 562, wireless network station 501 transmits an authentication requestmessage 551 to destination AP 562. Identity checking mechanism 525 usesa R0KH ID 551 a in authentication request message 551 to search for R0KHtable 515 and determines a setting parameter 555 of a handoff process.R0KH table 515 may include the IDs of all the R0KHs in the coveragerange accessible to the destination AP.

For example, in FIG. 6, when wireless network station 501 wants to movefrom AP₂ to AP₃, identity checking mechanism 525 checks and finds thatR0KH₂ ID is in the R0KH table at AP₃, it may determines that the FTauthentication is a setting parameter for the handoff process. On theother hand, when wireless network station 501 wants to move from AP₂ toAP₄, identity checking mechanism 525 checks and finds that R0KH₃ ID isnot in the R0KH table at AP₃, it may determines that the open systemauthentication is a setting parameter for the handoff process.

After receiving the authentication response message from the destinationAP, wireless network station 501 will execute the Fast BSS handoffprocess if the setting parameter in the response message is FTauthentication; on the other hand, wireless network station 501 willexecute the initial MD association handoff process if the settingparameter is the open system authentication.

Therefore, in FIG. 6, when wireless network station 501 makes anintra-MD movement, such as, from AP₂ to AP₃, the setting parameter inthe response message is FT authentication. Hence, wireless networkstation 501 will execute the Fast BSS handoff process. If wirelessnetwork station 501 makes an inter-MD movement, such as, from AP₂ toAP₄, the setting parameter in the response message is the open systemauthentication. Hence, wireless network station 501 will execute initialMD association handoff process. So, regardless the movement is aninter-MD or an Intra-MD movement, the wireless network station mayalways execute the suitable handoff process.

Because the change and update of the R0KHs within the MD cover range isless frequent, the contents of R0KH table 515 may be either dynamicallyor statically set in AP through the AP management system. The storing ofthe IDs of all the R0KHs may be done through the search of R0KH table515, and the AP management system allows the wireless network station toselect the handoff process. The exemplary structure of the disclosedembodiments in accordance with the present invention does not need tomanage MDID. Therefore, the execution of unsuitable handoff processcaused by the MDID collision will not occur. The present invention isalso applicable to the wireless network platforms of IEEE802.11rcommunication protocol.

According to the exemplary architecture of the disclosed embodiments,when the change or update of the R0KHs of a MD occurs, the IDs of theR0KHs in the AP may be dynamically or manually updated.

FIG. 7 further shows a schematic view of an exemplary flowchart of themethod for executing handoff process in wireless networks, consistentwith certain disclosed embodiments of the present invention. Referringto FIG. 7, after wireless network station 501 successfully executes datacommunication and connection with source AP 561, and when wirelessnetwork station 501 wants to move from source AP 561 to destination AP562, destination AP 562 has an R0KH table. The R0KH table stores the IDsof all the R0KHs accessible to destination AP 562 within the MD coverrange. The following steps 701-704 describe the execution of handoffprocess.

Step 702 is to select the handoff process. Through searching for the IDof the message to destination AP 562. The authentication request messagenotifies destination AP 562 to execute FT authentication. Theauthentication request message at least contains the information of aR0KH ID, but the MDID information is not necessary included in theauthentication request message.

Step 702 is to select the handoff process. Through searching for the IDof the R0KH in the R0KH table of destination AP 562, a suitable handoffprocess may be determined. After destination AP 562 receives theauthentication request message from wireless network station 501,destination AP 562 reads the R0KH ID in the message, and compares withthe R0KH table of destination AP to determine whether wireless networkstation 501 should execute initial MD association handoff process (step703), or Fast BSS handoff process (step 704).

When R0KH ID is not stored in the R0KH table of destination AP 562,destination AP 562 executes the open system authentication and repliesthe authentication response message to wireless network station 501, asin step 703. In the response message, the setting parameter is set asthe open system authentication. After wireless network station 501receives the response message, wireless network station 501 executes theinitial MD association handoff process. The description of the initialMD association handoff process is as in FIG. 2, and is omitted here.

When R0KH ID is already stored in R0KH table of destination AP 562,destination AP 562 executes the FT authentication and replies theauthentication response message to wireless network station 501, as instep 704. In the response message, the setting parameter is set as theFT authentication. After wireless network station 501 receives theresponse message, wireless network station 501 executes the Fast BSShandoff process. The description of the fast BSS handoff process is asin FIG. 3, and is omitted here.

In this manner, without the MDID for handoff process, the presentinvention may avoid the uncertainty of MDID. Also, through searching forthe R0KH table stored at AP, the wireless network station maydistinguish whether the movement is an inter-MD movement or an intra-MDmovement, and selects a suitable handoff process accordingly.

Although the present invention has been described with reference to theexemplary embodiments, it will be understood that the invention is notlimited to the details described thereof. Various substitutions andmodifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

1. An apparatus for executing handoff process in wireless networks,applicable to the movement of a wireless network station when saidwireless network station moving from a source access point (AP) to adestination AP, said apparatus comprising: a processor, executing anidentity (ID) checking mechanism, said wireless network stationtransmitting an authentication request message to said destination AP,said ID checking mechanism using a R0 key holder (R0KH) ID included insaid authentication request message to search a R0KH table of saiddestination AP for determining a setting parameter for a handoffprocess, and said wireless network station executing said handoffprocess according to said setting parameter; wherein said R0KH table ofsaid destination AP consisting of the IDs of all said R0KHs accessibleto said destination AP within the cover range of said destination AP. 2.The apparatus as claimed in claim 1, wherein said handoff process iseither an initial mobility domain (MD) association handoff process or aFast Basic Service Set handoff process.
 3. The apparatus as claimed inclaim 1, wherein each AP in said wireless network stores a R0KH tableconsisting of the IDs of all R0KHs accessible to said AP within thecover range of said AP.
 4. The apparatus as claimed in claim 1, whereinwhen said R0KH ID contained in said authentication request message isstored in said R0KH table, said setting parameter of said handoffprocess is fast transition authentication.
 5. The apparatus as claimedin claim 1, wherein when said R0KH ID contained in said authenticationrequest message is not stored in said R0KH table, said setting parameterof said handoff process is open system authentication.
 6. The apparatusas claimed in claim 1, wherein said apparatus is applied to IEEE802.11rprotocol.
 7. The apparatus as claimed in claim 1, wherein said movementof said wireless network station is either an inter-MD movement or anintra-MD movement.
 8. A method for executing handoff process in wirelessnetworks, applicable to the movement of a wireless network station whensaid wireless network station moving from a source access point (AP) toa destination AP, said method comprising: said wireless network stationtransmitting an authentication request message to said destination AP,said authentication request message containing a R0 key holder identity(R0KH ID); using said R0KH ID to search a R0KH table of said destinationAP for determining a handoff process, said R0KH table of saiddestination AP consisting of the IDs of all said R0KHs accessible tosaid destination AP within the cover range of said destination AP; whensaid R0KH ID not being stored in said R0KH table, said wireless networkstation executing an initial mobility domain (MD) association handoffprocess; and when said R0KH ID being stored in said R0KH table, saidwireless network station executing a Fast Basic Service Set (BSS)handoff process.
 9. The method as claimed in claim 8, wherein each AP insaid wireless network stores a R0KH table consisting of the IDs of allsaid R0KHs accessible to said AP within the cover range of said AP. 10.The method as claimed in claim 8, wherein when said R0KH ID contained isnot stored in said R0KH table, said destination AP replies anauthentication response message containing a setting parameter of saidhandoff process, and sets said setting parameter as open systemauthentication.
 11. The method as claimed in claim 8, wherein when saidR0KH ID contained is stored in said R0KH table, said destination APreplies an authentication response message containing a settingparameter of said handoff process, and sets said setting parameter asfast transition (FT) authentication.
 12. The method as claimed in claim8, wherein said source AP and said destination AP are both in the sameMD.
 13. The method as claimed in claim 8, wherein said source AP andsaid destination AP are in different MDs.
 14. The method as claimed inclaim 10, wherein said wireless network station executes an initial MDassociation handoff process.
 15. The method as claimed in claim 11,wherein said wireless network station executes a Fast BSS handoffprocess.